(Supported in part by NIH K11DE00257 and NIH RO1 AI29743 to N. Charon). The spirochete that causes periodontal disease, Treponema denticola, has a unique morphology. Outer most is a membrane sheath, and within this sheath are a helical shaped Cellular cylinder. At each end of the Cellular cylinder, bacterial flagella-like organelles, called periplasmic flagella are attached. These periplasmic flagella reside in the periplasmic space between the outer membrane sheath and Cellular cylinder. Genetic analysis has shown that these organelles are involved in the motility of spirochetes. In addition, several lines of evidence indicate that these periplasmic flagella propel the organisms by rotation in manner similar Borrelia burgdorferi, the lyme disease spirochete. We know that the periplasmic flagella not only play a role in motility, but influence the shape of the cellular domain where they reside. Using HVEM stereo pairs, we studied the configuration of the periplasmic flagella within the organism: How they wrap around the Cellular cylinder, and in which direction, i.e. clockwise and counter clockwise. Based on the results we obtained, we learned how these organelles influence the shape and the motility of the organisms. Goldstein, S.F., K.F. Buttle, and N.W. Charon. (Late 1996) Structural Analysis of the Leptospiraceae and borrelia burgdorferi by high-voltage electron microscopy. J. Bact., 178:6539-6545. Ruby, J.D., H. Li, H. Kuramitsu, S.J. Norris, S.F. Goldstein, K.F. Buttle and N.W. Charon. (1997) Relationship of Treponema denticola periplasmic flagella to irregular cell morphology. J. Bact., 179:1628-1635.